By Paul Wood, Master Gardener of Dakota County
MDA Certified EAB First Responder
This invader from China was first confirmed in Minnesota in 2009 in Southeast Minnesota. It was first found in the Twin Cities area later in 1990 in St. Paul’s and has been spreading ever since. It has been confirmed in other suburbs of St. Paul, in Bloomington ( Ft. Snelling), and most recently in Eagan (Lebanon Hills). It is probably elsewhere in the seven county metro area, but we just have not found it yet.
The Emerald Ash Borer (EAB) is incredibly destructive; the mortality of untreated ash trees is 100%. The State of Michigan alone has lost an estimated 40 million ash trees. Since Minnesota is home to an estimated 937 million ash trees there is more than just a little concern!
The EAB attacks ash of the fraxinus genus and nothing else. Here in Minnesota we have the Black Ash (f. nigra), the White Ash (f. americana), and the Green Ash (f. pennsylvanica). The Black Ash are prevalent throughout Minnesota except in the western counties, the White Ash are found along the river in southeast and central Minnesota, and the Green Ash is everywhere in the State. Here in the Twin Cities area there are thousands of ash trees because the Green Ash was primarily used to replace the elms that succumbed to Dutch Elm Disease.
If you have a Mountain Ash, don’t worry. Mountain Ash are not really ash trees; they are of the genus Sorbus. They are actually part of the Rose Family!
The EAB kills ash trees by, essentially, starving them to death. The female EAB beetle lays her eggs in the bark of ash trees. The eggs hatch into EAB larvae and work their way under the bark. The larvae survive by eating away at the phloem right under the bark leaving their characteristic S-shaped galleries. The eating of the phloem is what kills the tree because it is the phloem that carries the nutrients throughout the tree. The life cycle is completed by the larvae pupating and then emerging as the adult beetle and the process starts all over again.
It takes 3-5 years for EAB to kill an ash tree. Once the tree is infected, it is re-infected each season with more larvae, which eat more of the phloem. This process continues until there is not enough phloem to sustain the tree and the tree dies.
For the homeowner, detecting an EAB infestation is not easy. The beetles live in the tops of the tree and are about 1/2 of an inch long, so the chances of actually finding one are virtually nil. An infected tree does exhibit some characteristics like a dying or thinning crown, cracked bark, suckering, or epicormic branches. (Epicormic branches are the tuft like branch clusters on the trunk of a tree that are covered with leaves.) However, these are not conclusive evidence. A more consistent indicator is woodpeckers taking a more than casual interest in an ash tree. If your ash tree is being heavily visited by woodpeckers there is cause for concern.
Should you be alarmed? It depends. If there is an infestation within 10-15 miles then you need to be considering actions to take. If not, taking some defensive measures might be in order. If you do suspect that you have an infestation call your city forester or call the Arrest the Pest hotline at 888-545-6684 or email Arrest.thePest@state.mn.us.
Deciding whether to save or remove the tree is not necessarily and easy decision. It helps to ask yourself the following questions:
- Is this really a Green, White, or Black Ash tree? (This sounds funny, but….)
- What is the value of the tree? (Shades the house? Centerpiece of the front yard?)
- How many other trees are present? (One of many trees in the yard? Will it really be missed?)
- How healthy is the tree? (Is it old? Losing branches? In decline? Maintenance headache?)
- What is the cost of removal versus cost of treatment versus cost of replacement?
If you decide to try and save the tree, it is possible to treat ash trees for EAB even if the tree is already under attack. Most common defense that can be used by homeowners are the soil drenches available at Garden Centers. These drenches are sprayed on the soil around the tree out to the drip line where insecticide is then absorbed by the roots and circulated through the tree’s vascular system. Typically an annual application it needed. However, a word of caution. Check with your city to make sure use of drenches is not against city ordinances. Some available drenches contain the systemic pesticide Imidacloprid (one of the Neonicotinoids) and there is concern about run off into the storm sewer system and into our lakes and rivers. If it is legal to use the drench, apply it when there will be no rain for several days so that the drench is fully absorbed into the soil.
The best way to treat an ash is to have it professionally done. Professional treatment is more expensive than the drenches, but it is safer and the treatments last for two or three years. Cost is determined by the diameter of the tree in inches at “dbh” (e.g, about four feet up the trunk). Professional treatment is accomplished by drilling a small hole in the tree and injecting the insecticide directly into the tree. The tree will naturally heal the hole, so the tree will not be damaged. Alternatively, the insecticide is injected into the soil, but unlike the drench, this approach avoids any danger of runoff.
If you decide to have the tree professionally treated check with your city. Many cities have a list of tree companies licensed to treat ash trees within the city. Some even have pre-negotiated rates. Also, most cities have an EAB Plan and part of that plan may cover treating trees on public land and rights of way (easements). The beautiful ash tree in the front of your house may be treated by the city!
If you decide to remove the tree there are some things you need to be aware of. Dakota County, along with Hennepin and Ramsey counties, are quarantined by the Minnesota Department of Agriculture (MDA). This means that it is illegal to move ash material out of the county into a non-quarantined area except under rather stringent conditions. Further, ash material can only be disposed of at specific MDA sites. So taking the logs to the cabin up north is not an option! Finally, it is illegal to transport ash materials without proper safeguards from when the beetles are flying: May 1 through September 30 .
Bottom line: have the tree removed by a professional arborist. Again, check with your city for arborists certified to work within the city.
There is a wealth of EAB materials available on the Web. A good starting point is the MDA website www.mda.state.mn.us/eab . On this site you can find infestation maps, how to identify an ash tree, how to identify an EAB, quarantine areas and the regulations, suggested replacement trees, and ash disposal site.
The U of M Extension website (www.extension.umn.edu) has timely reference articles as well. Access the site and search for “EAB”.